This invention relates to the heating and melting of thermoplastic material from bulk containers. More particularly, this invention relates to the heating and melting of thermoplastic materials, such as hot melt adhesives, from containers, such as 55-gallon drums, 5-gallon pails, etc., such that the liquefied material may be pumped from the container for subsequent use by other application equipment.
There are a number of hot melt dispensers which liquefy and dispense thermoplastic materials, such as hot melt adhesives, which permit dispensing the material directly from the shipping container (drum, barrel, pail, etc.). One such common device includes an arrangement in which a heated element is lowered directly into the open end of the container for liquefying or melting the thermoplastic material in the region directly below this heating element. Typically, the heated element is a heated platen for liquefying the material so that a pump may pump the liquefied material to equipment for dispensing the material onto a substrate. Such apparatus would include those shown in U.S. Pat. Nos. 3,412,903; 3,637,111; 4,227,069; 4,195,755; and 4,661,688, as well as the Meltex.RTM. DG-21 and DG-201, and the Nordson 500 Series and 5500 Series Drum Melters.
Commonly, the dispensing apparatus includes a heated follower plate assembly, or platen assembly, which includes a pair of gaskets about its periphery, a pump for pumping the liquefied material and a lower heated section which when placed within the container liquefies the thermoplastic material for delivery through suitable passageways to the inlet of the pump. Typically, the lower portion of the follower plate or platen comprises a number of segments that are heated and are releasably attachable to the plate. Finally, either a platform may be provided by means of which the container is elevated or a mechanism may be provided by which the plate assembly is lowered into the container.
The lower heated segments of the plate or platen may be smooth or they may be finned in design. Typically, the flat heated surfaces are useful for liquefying material in which a demand or melting rate of the material is low while the finned design is used in those instances where higher melt temperatures and/or greater flow rates are required.
In operation, the platen is inserted into the container. O-ring seals, or gaskets, come into contact with the inner peripheral surface of the container that contains the adhesive. The container is not filled to capacity because the gaskets must first come into contact with the container to form a proper seal in which to remove the material. By positioning the gaskets at the lower portion of the platen the amount of unfilled space at the top of the container is minimized. This positioning allows the container to be filled with more material and leads to better overall use of the container.